The present invention relates to elevator systems. More particularly the invention relates to a termination for a flexible flat tension member.
A conventional traction elevator system includes a car, a counterweight, two or more ropes (tension members) interconnecting the car and counterweights; terminations for each end of the ropes at the connection points with the car and counterweights, a traction sheave to move the ropes and a machine to rotate the traction sheave. The ropes have traditionally been formed of laid or twisted steel wire which are easily and reliably terminated by means such as compression terminations and potted terminations.
Compression type terminations for steel ropes of larger diameters (conventional steel elevator ropes) are extremely effective and reliable. The range of pressures placed on such terminations is reasonably broad without adverse consequence. Providing that the pressure applied is somewhere reasonably above the threshold pressure for retaining the ropes, the termination is effective.
With an industry trend toward flat ropes, those ropes having small cross-section cords and polymeric jackets, significantly more criticality is involved in effectively terminating the same. More specifically, the polymeric coating can creep to even 50% of its original thickness when subjected to pressure. Prior art knowledge which teaches one to exceed a threshold is not all that is of concern for flexible flat tension members. Upper limits on compression are also important.
Since current knowledge in the art of tension member terminations is less than sublime for flexible flat tension members due both to the small cord diameter and the jacket properties discussed above, the art is in need of a tension member terminating device which specifically optimizes terminations of the flexible flat tension members currently emerging in the field.
According to the present invention, a compression termination device having a friction enhancing construction while reducing compressive forces applied to the tension member, comprises a load side plate, a cut side plate and a socket, a portion of which being receivable between said load side and cut side plates and a portion of which is bulb shaped. The plates and socket are of sufficient width to accept a flexible flat tension member of a selected width and are securable together by fasteners. In a condition where the fasteners are loose, the tension member is insertable between the load side plate and socket, toward and around the bulb and back up between the cut side plate and socket whereafter tightening of the fasteners produces significant frictional forces on the tension member to retain the same while compressive forces on the tension member are intentionally limited to about 2 Mpa on the load side of the device and 5 Mpa on the cut side of the device. Friction is increased by texturing the surfaces of the termination device with which the tension member makes contact. With compressive forces as stated, creep is minimized while the termination maintains a sufficient gripping force to provide a factor of safety (fos) of 12 to maintain adequate strength of the termination.
Since creep is a possibility even with Mpa levels at the stated limits, the invention optionally includes a structure providing resilience such that compressive force on the tension member will remain in the acceptable range even if creep does occur.
The termination of the invention further optionally includes a jamming device attachable to the cut end of the tension member. In the unlikely event of tension member slippage through the termination device, the jamming device will be drawn into the termination device and will prevent the tension member cut end from pulling through the termination device.